(a) Field of the Invention
The present invention relates to a finder, and, more particularly, to a real image zoom finder having its magnification varied by moving one or more optical elements.
(b) Description of the Related Art
Cameras are being made more compact and light-weight. Compact cameras require a small photographing system as well as a compact finder having a high magnification ratio.
The finder used in photographing systems generally comprises an objective lens group and an eyepiece lens group. An image of an object is formed through the objective lens group and is magnified by the eyepiece lens group, so that a user can observe the image of the object through the eyepiece lens group. However, without the eyepiece lens group, a user observes an inverted image because the objective lens group inverts the image upside down.
To make a camera as small as possible and to form an erect image, an optical system for erecting the inverted image formed through an objective lens group has been proposed. Such a system includes a finder using a mirror or a prism as an erecting system. Such a finder was disclosed in Japanese patent laid-open No. Hei 4-238314.
In this Japanese disclosure, an objective lens group includes first, second, third, and fourth lenses. The first lens has a negative refractive power. The second lens has a positive refractive power and varies the magnification of the lens group. The third lens has a positive refractive power and corrects aberration of the lens group. The fourth lens has a positive refractive power.
However, the disclosed finder is not suitable for a compact camera because a relatively long distance is required between a surface of the objective lens group closest to an object side and an image field. Also, the mechanical structure of the finder is complicated because the third lens moves a large distance, between 12 mm-21 mm. Consequently, it is difficult to manufacture the finder. In addition, it is difficult to manufacture the finder because each lens in the lens group is made of a different material.